1. Field of the Invention
The present invention relates to an image sensor having a wave guide as a traveling path of incident light and a method for manufacturing the same, and more particularly, to an image sensor having a wave guide, in which a separate wiring layer is formed over a photodiode so that etching uniformity is secured and the generation of dark current by plasma ions during an etching process is prevented when forming a wave guide through etching, and a method for manufacturing the same.
2. Description of the Related Art
Image sensors are semiconductor devices which convert an optical image into electrical signals. Representative image sensors include a charge coupled device (CCD) and a CMOS image sensor.
Between these two image sensors, the CMOS image sensor stands for a device which converts an optical image into electrical signals using a CMOS manufacturing technology. The CMOS image sensor adopts a switching scheme in which MOS transistors are formed by the number of pixels and outputs are sequentially detected using the CMOS transistors.
When compared to the CCD image sensor which has been widely used heretofore as an image sensor, in the CMOS image sensor, a simple driving scheme is used, and various scanning schemes can be realized. Further, since a signal processing circuit can be integrated in a single chip, miniaturization of a product is made possible, and since a compatible CMOS technology is employed, the manufacturing cost can be reduced and the power consumption can be significantly decreased.
The CMOS image sensor is composed of a photodiode which detects light and a CMOS logic circuit which converts detected light into an electrical signal as data. In order to improve the light sensitivity of the image sensor, efforts have been made to increase a ratio between the area of the photodiode and the area of the entire image sensor (that is usually called a fill factor). However, because the CMOS logic circuit cannot be omitted, difficulties necessarily exist in increasing the ratio.
Under these situations, light condensing technologies have been disclosed in the art, in which paths of light incident on points other than the photodiode are changed to be directed toward the photodiode so as to elevate the light sensitivity. Representative technologies include a microlens forming technology and a technology using a wave guide.
In the case where light is condensed using a microlens, as the number of integrated pixels increases these days, the distance between the microlens and the photodiode disposed under the microlens increases gradually as well. Due to this face, since a focus cannot be formed on the photodiode, a problem is caused in that light having passed through the microlens cannot be effectively transferred to the photodiode.
Meanwhile, research has been directed toward the technology for providing a wave guide in the traveling path of incident light and allowing light incident on the photodiode to pass through the wave guide, thereby minimizing the loss of incident light and suppressing a crosstalk between adjacent pixels.
FIG. 1 is a cross-sectional view illustrating a conventional image sensor having a wave guide.
Referring to FIG. 1, it can be seen that a conventional image sensor having a wave guide is configured in such a way that an interlayer dielectric 16 formed over a photodiode 11 is etched and a wave guide 19 is formed thereby.
However, in the conventional image sensor having a wave guide, since an amount of the interlayer dielectric 16 to be etched when forming the wave guide 19 is considerable and an etching depth is substantial, etching uniformity cannot be secured. Such non-uniformity leads to the non-uniformity of the photodiode 11, whereby the characteristics of the image sensor are likely to deteriorate.
Also, an amount of plasma ions needed in an etching process for forming the wave guide 19 increases, and a portion of the plasma ions is introduced into the photodiode 11 and serves as a factor for causing a defect in the photodiode 11, whereby the characteristics of the entire image sensor are likely to further deteriorate.